How does coercion affect an acknowledgment according to the commentary in Fath al-Qadir?

Kitab al-Iqrar: Capacity, Unspecified Rights, and Amounts in Admissions

• Coercion automatically doubles the sum
• A coerced admission is not treated as an ordinary voluntary admission
• Coercion matters only for witnesses, never for the admitting party
• Coercion permanently extinguishes every claimant’s right